The present invention relates to a semiconductor integrated circuit device and a semiconductor memory system, and, particularly, the invention relates to a technique effective for use in devices which need minute or micro and highly-accurately controlled delay signals. This invention also relates to a clock synchronous circuit having a quick response and to high accuracy and a technique effective for use in a semiconductor integrated circuit device, such as a synchronous DRAM (Dynamic Random Access Memory) equipped with a clock synchronous circuit.
An array oscillator disclosed by ISSCC has been known as an example of a circuit for obtaining a time resolution of a few 10 psec (picoseconds). In this known type of array oscillator, the same ring oscillators are arranged in large numbers in a column direction and are connected in a ring form using one input of each individual stage as two inputs, and the outputs of the respective stages are respectively supplied to other inputs of adjoining stages, and they are also connected in ring form even in a row direction.
Such an oscillator has been described in ISSCC 93/ANALOG TECHNIQUES/PAPER TA7.5, pp. 118-119, 1993 and ISSCC/SESSION 18/MEMORIES WITH SPECIAL ARCHITECTURES/PAPER FP18.5, pp 308-309, 1995, and Japanese Published Unexamined Patent Application No. Hei 8-78951.
A clock synchronous circuit excluding a feedback loop like a synchronous mirror delay (SMD) is characterized in that the time (lock time) necessary for synchronization is short, as in the case of 2 to 3 cycles. According to this feature, the lock time can be shortened by measuring the cycle of an input clock as the number of stages of delay circuits or coarse delays. The time resolution of this measuring circuit is determined depending on a delay time per stage corresponding to a component of each delay circuit. The time resolution is normally on the order of a delay time corresponding to two stages of CMOS inverters. Japanese Published Unexamined Patent Application No. Hei 8-237091 is an example of a clock synchronous circuit using such an SMD.